This invention relates to phased array antennas, and more particularly to a beam steering controller used with a phased array antenna. The beam steering controller calculates the necessary phase shift data for each of the antenna elements of the antenna needed to point the antenna in a desired pointing direction while requiring a significantly lesser amount of data to be supplied thereto from an independent controller system disposed remotely from the antenna.
Previously developed phased array antenna beam steering controller designs have relied on antenna elements (i.e., xe2x80x9cmodulesxe2x80x9d) spaced at regular X and Y intervals in the antenna. Phase shift data is calculated for each element based on a constant delta phase shift in the X and Y directions (from row to row and column to column). Also, previous designs of phased array antennas have required each phase shift value for each antenna element of the antenna to be transmitted over a cable from an internal controller in the vehicle (such as an aircraft) to the external beam steering antenna. For a 1500 element phased array antenna, six twisted pairs of conductors (100 foot cable, 5 Mbit/sec RS-422) have been required to transmit the phase data from the internal controller within the vehicle to the external beam steering controller of the antenna to support a one millisecond beam update rate. The existing external beam steering controller used with present day phased array antennas decodes messages from the internal controller and serially loads phase shift data into each element in the antenna through a matrix of rows and columns of data and clock signal lines.
Accordingly, it would be highly desirable to provide a phased array antenna having an external beam steering controller which is capable of generating the needed phase shift data for each element of the antenna without requiring the heretofore very large amounts of phase shift data to be supplied from the internal controller disposed remotely from the antenna. More specifically, it would be highly desirable to provide an external beam steering controller which is capable of determining the needed phase shift values to be applied to each antenna element from just the spherical pointing information representing the desired pointing angle of the antenna. Such a beam steering controller would dramatically reduce the amount of electrical cabling required to supply the phase shift data to each antenna element of a phased array antenna incorporating hundreds or thousands of independent antenna elements. This would dramatically reduce the number of bits of information required to be sent from the remote (i.e., internal) controller to the external beam steering controller. Also, this capability would permit the data to be transmitted at a fraction of the data rate that would otherwise be required if all of the needed phase shift data was being supplied from the remote controller.
The above and other objects are provided by an advanced external beam steering controller and method for use with a phased array antenna, in accordance with preferred embodiments of the present invention. In one preferred form the external beam steering controller incorporates a memory for storing X, Y and Z access antenna element geometry information representative of the location of each antenna element in X, Y and Z coordinates, relative to a pre-determined center of the antenna. The advanced external beam steering controller (AEBSC) is also in communication with the remote (i.e., internal) controller and receives information from the remote controller which contains the X, Y and Z axis phase gradients for a desired pointing angle of the antenna. The AEBSC uses the phase gradient information and the element geometry information stored in its memory to calculate the individual element phase shift values required to point the antenna in accordance with the desired pointing angle.
It is a particular advantage of the present invention that the antenna element geometry information is unique to the antenna and can represent antenna elements located at random (i.e., non-uniform) X, Y and Z locations. Put differently, the independent antenna elements can be arranged in patterns which deviate from the typical X, Y uniform grid arrangement. Thus, the antenna element geometry information allows for a plurality of antenna elements to be arranged to form square, circular or other antenna shapes. Furthermore, the antenna elements do not need to be positioned in the traditional X-Y grid, with the rows of elements being parallel to one another and the rows and columns intersecting in perpendicular fashion. Since the precise location of each antenna element, relative to the center of the antenna, is stored in the memory of the AEBSC, positioning of the elements in virtually any non-uniform configuration is permitted.
In one preferred form of the invention, the AEBSC receives spherical coordinate pointing information from the remote controller. This information comprises values representing the fraction of a wavelength of phase shift per wave length of displacement of a given antenna element along each of the X, Y and Z axes of the antenna. These values are transmitted as 16 bit, signed 2""s complement binary values with the least significant bit (LSB) representing 2xe2x88x9210 of a wavelength at the center operating frequency of the antenna. Such binary values require a minimum of 10 bits to the right of the binary point. A sign bit and 5 non-fractional bits are preferably provided to the left of the binary point to support scaling the DX, DY and DZ fractional wavelength phase shift values up or down to support other frequency bands (i.e., frequency bands different than the antenna center frequency). This dynamic range and precision supports an antenna with dimensions of greater than 32 wavelengths in the X and Y directions.
The AEBSC then calculates the phase for each element of the antenna from the stored element geometry information and the pointing information provided by the remote controller to determine an element delay value representing the delay in wavelengths required for the signal from a given antenna element to the antenna center, in order to sum in-phase with signals from the other antenna element. The AEBSC then determines an element phase shift value for each antenna element by rounding the element delay to a given number of bits and then truncating that number to one wavelength.
The present invention thus allows phase shift values to be calculated by the AEBSC and supplied to a large plurality of antenna elements, while supplying only the spherical coordinate pointing information from the remote controller. This dramatically reduces the amount of electrical cabling required for the antenna, as well as reducing the required data rate at which the information from the remote controller needs to be supplied to the AEBSC.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.